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From the Departments of Neurology and Neurological Surgery (Neurology) (Drs. Racette, Mink, Videen, Perlmutter, and L. McGeeMinnich), Pediatrics (Dr. Mink), Anatomy & Neurobiology (Drs. Mink and Perlmutter), American Parkinson Disease Association Advanced Center for Parkinson Research (Drs. Racette, Mink, Perlmutter, and L. McGeeMinnich), and the Mallinckrodt Institute of Radiology (Drs. Moerlein, Videen, and Perlmutter), Washington University School of Medicine, St. Louis, MO.
Address correspondence and reprint requests to Dr. Brad A. Racette, Washington University School of Medicine, 660 South Euclid Avenue, Box 8111, St. Louis, MO 63110; e-mail: racetteb{at}neuro.wustl.edu
| Article Abstract |
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| Introduction |
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A number of health problems are attributed to welding fumes. Welding may cause acute upper respiratory symptoms,5 pulmonary edema,6 pulmonary fibrosis,7 and lung cancer.8 Welding has also been associated with genitourinary9 and laryngeal10 cancers. Actinic keratoconjuctivitis (welders flash)11 and cataract formation12 from ultraviolet radiation may be produced by the arc if eye protection is not worn. Neurologic complications of welding exposures include encephalopathy, probably from exposure to the fume (fume fever),13 and lead poisoning caused by heating lead-based paint.14
The materials safety data sheet (MSDS) for welding consumables lists parkinsonism as a potential hazard of welding. Evidence supporting these claims consists of several case reports15-18; however, no established relationship between welding exposure and development of symptoms has been shown. Most reported patients had atypical features, including cognitive abnormalities, disturbances of sleep, peripheral nerve complaints, and mild motor slowing.15,19 Manganese may be the toxic agent in welding fumes,19,20 but welders exposed to manganese fumes in one study did not have higher blood concentrations of manganese than controls.19 We have studied welders who developed parkinsonism to determine whether the symptoms and disease course in these individuals were different from those in controls with idiopathic PD.
| Methods. |
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The first control group of 100 patients diagnosed with idiopathic PD23 was sequentially ascertained from the Movement Disorders Center. The second control group from the same center included six patients with PD age- and gender-matched to each of the welders with parkinsonism.
Statistical analysis.
Age at onset in the two groups and duration of disease was compared with a two-tailed, un-paired Students t-test. The distributions of the Hoehn and Yahr in the three groups were compared using a MannWhitney U test. We used a
2 analysis to compare the frequency of individual clinical features between controls and welders. The Bonferroni correction was applied to correct for multiple comparisons; all p values obtained from comparison of clinical features were multiplied by 12, corresponding to the number of comparisons made between the welders and two control groups. All p values reported are corrected values.
6-[18F]fluorodopa ([18F]FDOPA) PET studies. [18F]FDOPA PET scans were performed in two welders (aged 44 and 46 years at time of scan) and in 13 subjects (mean age, 49 years; range, 41 to 55 years) with typical idiopathic PD. These "control" subjects with PD had an average duration of symptoms of 2 years, closely matching the two welders. Similarly, they had asymmetric symptoms including bradykinesia, rigidity, and resting tremor (only one did not have resting tremor). Patients fasted overnight, with no PD medications taken for 12 hours before the study. PET scans were acquired by using a Siemens/CTI 953B scanner (Knoxville, TN) in 3D mode.24 Each subject took carbidopa 200 mg 1 to 2 hours before the study. A lateral skull radiograph recorded the position of each subjects skull with respect to the PET images.25 Attenuation factors were measured by using a transmission scan made with rotating rod sources of 68Ge. [18F]FDOPA was prepared as previously reported.26 After injection of [18F]FDOPA (4.65 to 5.00 mCi with a specific activity of approximately 365 Ci/mol), we collected 30 sequential PET images, beginning with 2-minute frames and increasing to 5 minutes. Reconstructed resolution of the images was approximately 5 mm full width at half maximum in the transverse plane. All frames were realigned to correct for head movement during the study, with reference to the first frame in which counts filled the brain. Each sequential frame was aligned to its preceding frame by use of automatic image registration.27 Before alignment, frames were resampled to remove bias caused by pixelization.28 Resampled frames were then smoothed (by AIR, 5-mm 3D blur) and the mean bidirectional fit was computed. Each frame was resliced exactly once by use of the combination of transformation matrices of all preceding frames plus the inverse of the resampling matrix.
Regions of interest, including caudate (10 x 10 x 13.5 mm), anterior putamen (10 x 10 x 13.5 mm), posterior putamen (10 x 10 x 13.5 mm), and occipital region (27 x 13 x 4.5 mm), were identified by a blinded rater who used a stereotactic method independent of the appearance of the images.25 The striatal regions included four contiguous PET slices. An influx constant Ki was calculated,29,30 with the occipital region as the input. We calculated Ki by using data from 24 to 94 minutes after injection. These PET studies were approved by the Human Studies committee and the radioactive drug research committee of Washington University School of Medicine. All participants gave written informed consent.
| Results. |
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| Discussion. |
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Our clinical observations and PET findings suggest that the pathophysiology of welding-related parkinsonism is similar to idiopathic PD, but we do not have pathologic confirmation of the diagnoses. Nevertheless, we speculate that the younger age at onset may be attributable to the effects of an accelerating agent from welding in a potentially "at-risk" patient who might otherwise develop PD with a later age at onset. Alternatively, parkin-associated parkinsonism could cause this phenotype in either familial or sporadic young-onset parkinsonism.33 Expression of a genetic parkinsonism could be mediated by an environmental modifier. If welding contributes to the parkinsonism in these patients, presumably the accelerant would be inhaled, and the element in the inhalant most consistently associated with an extrapyramidal syndrome is manganese.
A variety of occupational manganese exposures are associated with a primarily extrapyramidal presentation called manganism.34-38 The syndrome, best characterized in Moroccan manganese miners, includes progressive parkinsonism, dystonia, and neuropsychiatric symptoms.34 Those exposed to manganese while working in the steel industry also may develop progressive parkinsonism.35-37 Levodopa responsiveness in these parkinsonian subjects is transient and not associated with motor fluctuations.39-41 Although our patients differ from the classic scenario of manganese exposures, this does not necessarily disprove the association. It is possible that our patients experienced a lower level of inhaled manganese exposure compared with occupations involving crushing of manganese ore (miners), because ore crushing produces higher air concentrations of manganese.16 Low-level, long-term exposure over many years may be more analogous to unknown environmental triggers hypothesized to cause PD.42
Our two welders who had PET had asymmetric reduction of striatal [18F]FDOPA uptake with greater reduction of uptake in posterior putamen, findings that are typical of idiopathic PD.43 Although there are only two subjects, the welders did have greater asymmetry of caudate [18F]FDOPA uptake than our 13 subjects with PD. An older study found normal striatal [18F]FDOPA uptake in people with manganism; however, because of the relatively low resolution of the PET scanner in that study, the authors were only able to calculate uptake in left and right striatum and could not identify specific reductions in smaller regions such as posterior putamen.44,45 It is also not clear whether the four subjects in that study had clinical manifestations similar to ours. They did report that all had bradykinesia, rigidity, and "gait abnormalities." Two had mild rest tremor, but the degree of asymmetry and response to levodopa were not addressed,46 making it difficult to directly compare our results. Typical manganism may cause characteristic symmetric hyperintensities in the globus pallidus on T1-weighted MRI that resolve when the exposure is eliminated.15,45,47,48 However, the sensitivity of the T1 signal changes for manganism is unknown. None of our welders had MRI-identified abnormalities in the basal ganglia, but the PET studies provided results typical of idiopathic PD. These findings suggest that our welders have a pathologic condition similar to idiopathic PD.
Our study suggests that welding may be a risk factor for a parkinsonism syndrome that is associated with reduced [18F]FDOPA uptake and is clinically indistinguishable from idiopathic PD except for age at onset. We believe that welding exposure acts as an accelerant to cause PD. Our findings do not prove that manganese is the toxic agent, and other components of the fume could be responsible for parkinsonism in welders. Further studies are necessary to clarify this important issue. A detailed clinical evaluation of career welders compared with age-matched controls in a proper epidemiologic study will be essential to prove the relationship between welding and parkinsonism. If further studies prove an increased risk of parkinsonism in welders, welding may be the first example of an environmental risk factor for idiopathic PD.
| Acknowledgments |
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The authors thank John Hood, Jr., and Terry Anderson for expert technical assistance, William H. Margenau and David C. Ficke for radioisotope production, and Dr. Tamara Hershey for statistical assistance.
| Footnotes |
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| References |
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